"Apply modifiers" button not appearing?
The apply modifier button will be on the modifier.
Blender 2.9x
In Blender 2.9x click on the top triangle to apply the modifier, or use Ctrl+A.

See: How to apply a modifier in V2.9+
Blender 2.7x

You have to be in object mode to apply modifiers. Applying the  modifier does not work on multiple selections, only the active object gets applied.